Pencil lead is graded by hardness: a greater percentage of clay results in a harder lead. H (harder), F, HB and B (softer) are pencils of average hardness. Pencils ranging from 2B to 9B are softer still and are used for sketching; 2H to 9H are harder than average. A common American #2 pencil is equivalent to HB.

This is a nice lead thickness if one finds the .5mm too thick. No need to
purchase a .4mm specific pencil. I use these .04mm leads in my pentel P205,
Graphlet PG305, Sharplet-.05 and mini-Sharp .5mm mechanical pencils without nary
a problem. Should work great in all the other Pentel .5mm's as well. No slop and
no breakage. It works perfect!